Field of the Invention
The present invention relates to a ferroelectric thin film-forming sol-gel solution. Specifically, the invention relates to a ferroelectric thin film-forming sol-gel solution capable of obtaining a crack-free and dense ferroelectric thin film after pre-baking and baking when a single layer thereof having a thickness of greater than several hundreds of nanometers is formed by coating a ferroelectric thin film-forming sol-gel solution once using a chemical solution deposition (CSD) method.
Priority is claimed on Japanese Patent Application No. 2013-056229, filed on Mar. 19, 2013, the amount of which is incorporated herein by reference.
Description of Related Art
In the related art, in a case where a PZT-based ferroelectric thin film (hereinafter, abbreviated as “PZT film”) is formed on a substrate using a CSD method such as a sol-gel method, when a single layer of the film is formed in each coating process using a PZT-based ferroelectric thin film-forming sol-gel solution (hereinafter, abbreviated as “sol-gel solution”), the thickness of the single layer is limited to about 100 nm. The reason is that, when a film having a thickness of greater than 100 nm is pre-baked and baked, tensile stress generated in a PZT film is non-uniform in the same film, and thus cracking frequently occurs in the same film. Accordingly, currently, in order to obtain a PZT film having a thickness of several micrometers, it is necessary that the thickness of a single layer be further decreased and that pre-baking and baking be repeated while performing a coating process several tens of times. However, with such a method, production efficiency decreases, which leads to an increase in film forming cost.
In order to solve the above-described problem, disclosed is a sol-gel solution capable of obtaining a thick film of which a single layer having a thickness of 200 nm or greater is formed in each coating process of the sol-gel solution by using propylene glycol as an organic solvent for preparing the sol-gel solution (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2001-261338 (claim 1, paragraphs [0016] to [0024], and Table 1)). In addition, disclosed is a method capable of forming a thick single layer in each coating process of a sol-gel solution, in which a high-molecular compound is added to a high-concentration sol-gel solution to release tensile stress generated during film formation (for example, refer to J Sol-Gel Sci Technol (2008) 47:316 to 325)
In addition, Published Japanese Translation No. 2001-521976 of the PCT International Publication discloses a configuration in which N-methyl pyrrolidone is used as a solvent of an ink composition for ink jet printing, the solvent dispersing a core-shell polymer binder and ferrite powder (for example, refer to paragraphs [0013] and [0188]). However, the composition disclosed in Published Japanese Translation No. 2001-521976 of the PCT International Publication is a composition for ink jet printing, and smearing resistance is improved by the core-shell polymer binder. That is, the object and the configuration of this composition are completely different from those of a sol-gel solution according to the invention described below. Further, the composition disclosed in Published Japanese Translation No. 2001-521976 of the PCT International Publication is a composition formed of a dispersion obtained by dispersing ferrite powder in a solvent, and the configuration thereof is completely different from that of a composition formed of the sol-gel solution according to the invention in which a metal alkoxide and the like are used as raw materials.